In tire manufacturing, numerous tire components are formed of a plurality of rubber parts. Rubber tire components such as the tire apex, sidewall, and tread are formed by an extrusion process. One type of extruder typically used in tire manufacturing is a screw extruder. The screw extruder typically has a long chamber with a screw centered in the channel, wherein the screw masticates the rubber. The end of the channel typically has a die having a hole formed therein. The shape of the hole dictates the cross-sectional shape of the rubber part to be made. The extruder pressure forces the rubber through the small die hole forming the part to be made in a continuous manner The desired rubber part is obtained by cutting the extruded part to a given length.
The invention relates to coextrusion of tie components. Co-extrusion is the manufacture of a multi-layered rubber composite in a single operation. The multi-layered rubber composite is composed of at least two individual rubber compositions configured as rubber layers, wherein each rubber layer extends through the rubber composite thickness from one side to the other opposing side. The multi-layered rubber composite is prepared by co-extruding at least two individual rubber compositions, via an individual extruder for each rubber composition, to an internal cavity of a head. The head is comprised of an internal cavity which contains flow channels for guiding the at least two individual rubber compositions to form said multi-layered rubber composite through a splice bar and die, forming a composite strip in a single manufacturing step.
The problem of smear may occur as a side effect of co-extrusion. Smear is the appearance of a thin layer (usually a few microns) of a compound at an unexpected location of the multi-layered rubber composite. Smear is generally undesired, and is usually the result of rubber flow at junction or gaps between parts of the co-extrusion equipment. Thus it is desired to have improved manufacturing equipment which substantially reduces or eliminates smear in component co-extrusion manufacturing.